Traditional auxiliary-force control methods for electric bicycles provide auxiliary force for the pedaling force of a user when output power based on torque. As shown in FIG. 1, a user pedaling-force line a indicates the pedaling force exerted by the user, and auxiliary-force line b indicates the auxiliary force provided by a torque sensing device based on the pedaling force.
However, the torque sensing device is vulnerable to vibrations, impact, moisture and the like and may result in sensing errors. In addition, the torque-sensing device tends to be heavy, which consumes more auxiliary power and user's physical strength. Further, the torque-sensing device also requires frequent calibration by maintenance personnel in order to maintain accuracies up to standard. Moreover, a typical mechanical torque-sensing device has the characteristic of signal delay, so users cannot immediately receive the desired auxiliary power. Most importantly, the torque sensing device is much more expensive than a pedal-rotating speed sensor, which is a burden for both manufacturers and consumers.
Auxiliary power of electric bicycles may also be provided based on sensing by the pedal-rotating speed sensor, as shown by auxiliary-power line c in FIG. 1. However, it can be seen from FIG. 1, in the case of providing auxiliary power based on sensing by the pedal-rotating speed sensor, auxiliary power cannot be automatically adjusted according to the change in the slopes of the roads. As a result, too much or too little power may sometimes be provided, such that the users may not be able to pedal smoothly and energy is wasted.
In the other aspect, traditional energy recovery control techniques for electric bicycles are mostly achieved through flywheel diodes. However, if recovery time becomes long, power loss will also increase, so energy may be dissipated in the form of heat, rendering a poor recovery result.
Taiwan Patent Nos. 381997, 572838, M324630 and 470037 are prior arts related to auxiliary power techniques, wherein Patent No. 381997 provides auxiliary power output by the transmission principle of a planetary gear set of double input shafts in conjunction with motor rotation speed controller; Patent No. 572838 provides an energy-feedback electric vehicle with non-contact auxiliary brake device, which controls reverse current of the motor by switching power transistors such that excessive kinetic energy is converted into electrical energy; Patent No. M324630 proposes using gear tachometer in conjunction with a torque sensor as the input control signals for the motor, as well as techniques for displaying information such as assist rate, mode, speed, mileage etc.; and No. 470037 proposes a technique for processing received ride information in order to provide appropriate auxiliary power to users.
In addition, U.S. Pat. Nos. 6,131,683, 5,857,537, 6,412,800 and 7,185,726 also disclose techniques related to auxiliary power, wherein U.S. Pat. No. 6,131,683 combines a control circuit, a speed/torque sensor and a speed reduction mechanism for driving the wheels; U.S. Pat. No. 5,857,537 proposes driving the wheels by motor inside the wheels; U.S. Pat. No. 6,412,800 relates to a modular design of mechanisms such as an electric motor, a controller and a speed change gear set; and U.S. Pat. No. 7,185,726 discloses providing a driving unit and related connection mechanisms in the rear panniers of the bicycle.
However, only a few of these prior arts use rotating speed sensors for providing motor driving signal, and most of them use torque sensing devices for providing motor driving signal, and drive the transmission system in conjunction with the design of gear sets. Such approaches cannot avoid the various shortcomings of the torque-sensing device as mentioned earlier. Moreover, these Taiwan and United State patents fail to offer good performance in terms of energy recovery.